1. Field of the Invention
This invention relates to an image information input system, and more particularly relates to a system for inputing image brightness information into an exposure control system for use in a photographic camera or a photographic printer in which various parts of an image are differently weighted for providing modified image information according to the kind of the scene of the image.
2. Description of the Prior Art
There have been known various kinds of light measuring system such as averaged light measuring, center-weighted measuring and partial measuring. In the averaged light measuring, the averaged value of the amount of light from the whole scene viewed by the taking lens of the camera is measured by use of a photodetector which has substantially the same angle of view as that of the taking lens. In this light measuring system, it is impossible to obtain a proper exposure of the subject matter of photography in case that there is a bright background behind the subject matter such as the sky or back light. Though it is known to correct the exposure controlled by the averaged light meaasuring by use of a correction means which effects increase or decrease of the measured values, it is troublesome to operate such a correcting means and it is difficult to accurately correct the exposure by the optimum amount.
In the center-weighted measuring, the central part of an image is weighted in comparison with the marginal part. In the partial measuring, only a part of an image is measured. These two light measuring systems are based on an empirical rule that the subject matter of photography is normally located around the center of the scene aimed by a camera and weights the central part in comparison with the marginal part to lower the weight of the brightness information of the marginal part of a scene. Accordingly, these two light measuring systems are disadvantageous in that the exposure cannot be properly controlled based thereon in case that the subject matter is not located around the center of a scene or the difference in brightness between the central part and the marginal part is too large.
Beside the above mentioned light measuring systems, there have been known in the art to use the maximum and minimum values of the brightness of some parts of a scene to obtain more practical information as disclosed in Japanese Unexamined Patent Publication Nos. 92622/1976, 13412/1978, 91224/1979 and Japanese Utility Model Publication No. 9271/1976, and to divide the scene into the upper half and the lower half to obtain information of these halves separately as disclosed in Japanese Unexamined Patent Publication Nos. 75442/1976, 96829/1978, 90926/1974, 90927/1974, 71834/1978, 118127/1978 and Japanese Patent Publication No. 8516/1971.
The above-mentioned various kinds of light measuring systems, however, are all disadvantageous in that it is very difficult to provide the optimum light measuring or the optimum image information for any kind of scene. In other words, the above systems are effective for a few particular kinds of scene but not for all kinds of scene, because the photodetectors and the measured value operating circuit are always the same for any kind of scene.